The present invention relates to a device for manufacturing a semiconductor device and a method of manufacturing the same. More particularly, it relates to property control of a surface of a semiconductor layer and a film formed thereon in a manufacturing process performed by using a clustered manufacturing device in an atmosphere insulated from an external space.
As the packaging density of a semiconductor integrated circuit has increased in recent years, miniaturization and higher performance have been required of an element composing a MOS device, such as a transistor. However, the miniaturization of an element such as a transistor should not reduce the reliability of the whole device. Therefore, both miniaturization and increased reliability are required of each component of an element such as a transistor.
In particular, a gate insulating film (gate oxide film), which is an essential component of a MOS device, has rapidly been reduced in thickness. It is expected that an extremely thin insulating film with a thickness of 4 nm or less will be used in the twenty-first century. Since the properties of the gate insulating film are said to determine the properties of the MOS transistor and the electric properties of a semiconductor integrated circuit, the formation of an insulating film with excellent properties has been in great demand.
It has been proved that the properties of an insulating film are largely dependent on the surface state of a semiconductor layer before the insulating film is formed thereon. Accordingly, there has been studied a cleaning method for improving the properties of the semiconductor layer or the like. For example, it has been reported that the use of a cleaning method (pregate cleaning process) which minimizes the undulations of a surface of a Si substrate allows the formation, on the laboratory level, of a high-quality gate oxide film with an extremely small thickness of about 1.2 nm.
There has also been reported a clustered manufacturing device which allows sequential process steps from pregate cleaning to gate insulating film formation to be performed without exposing wafers to an atmosphere and thereby prevents the formation of a natural oxide film and the deposition of a contaminant resulting from exposure to the atmosphere (Document 1: Schuegraf et. al., IEEE/International Reliability and Physics Symposium 97, p. 7). It has been proved that a high-quality gate insulating film can be formed by the manufacturing process using the clustered manufacturing device. The use of the clustered manufacturing device is particularly desirable in the step of forming a gate insulating film having a reduced thickness of 4 nm or less.
On the other hand, property control of the gate insulating film in a MOS device has been performed conventionally by forming an element such as a MOS capacitor or MOS transistor and analyzing the electric properties of the element. If any trouble occurs in the step of forming the gate insulating film, the procedure is followed in which the trouble is found by evaluating the electric properties of the MOS capacitor or the like that has been formed previously, diagnosing the cause of the trouble, and practicing a troubleshooting method. As a result, a large quantity of gate insulating films with degraded electric properties are formed consecutively till the trouble is found, which reduces production efficiency.
If an ellipsometer used conventionally for measuring a film thickness in the manufacturing process is used to measure the thickness of a thin film, it does provide a measured value, but the minimum film thickness that can be measured with reliability is on the order of 10 nm. It can hardly be said that a film thickness smaller than 10 nm is measurable with sufficiently high accuracy. Thus far, a reliable evaluation method which is usable for an extremely thin film with a thickness of about 4 nm or less in the manufacturing process has not been established yet.
Although the electric properties of a MOS capacitor or the like formed on a wafer are measured after a large number of sequential process steps were performed with respect to the wafer in the process using the clustered manufacturing device described above, there is no method of controlling the condition of the wafer in the course of the process steps. Despite the fact that a high-quality gate insulating film is formable on the laboratory level, there is no guarantee, under present circumstances, that high-quality gate insulating films can be formed in the process of mass-producing MOS devices even by using the clustered manufacturing device.
It is therefore a first object of the present invention to provide a method of manufacturing a semiconductor device incorporating an optical evaluation method which can provide sufficient reliability and accuracy in measuring the properties of an extremely thin film.
A second object of the present invention is to provide a method and device for manufacturing a semiconductor device which allow optical measurement of the properties of an insulating film, especially the thickness thereof, and provide a method of property control in sequential process steps from pregate cleaning to insulating film formation, which are performed by using a clustered manufacturing device.
A device for manufacturing a semiconductor device of the present invention is a clustered device comprising: a plurality of processing rooms for processing a wafer having a semiconductor region; a shared container enclosing a space containing the plurality of processing rooms such that the space is held in an atmosphere disconnected from an external space; transporting means for transporting the wafer within the shared container; and optical measuring means for optically evaluating a surface state of the wafer being disposed at any site in the shared container.
The arrangement allows optical evaluation of the surface state of a wafer in a situation unaffected by a natural oxide film formed on the wafer or contamination deposited thereon by exposing the wafer to the external space. By thus optically evaluating the surface state of the wafer after the removal of the film or after the formation of the film, the thickness of an oxide film or the like can be measured with high accuracy. Since the wafer need not be extracted, for optical evaluation, to the outside of the shared container, the process of manufacturing a semiconductor device can be controlled properly by using in-line evaluation without adversely affecting the wafer in the manufacturing process.
In the device for manufacturing a semiconductor device, the optical measuring means can be comprised of: a first light source for generating exciting light; a second light source for generating measuring light; a first light guiding member for intermittently irradiating the semiconductor region of the wafer in the shared container with the exciting light generated from the first light source; a second light guiding member for irradiating the semiconductor region with the measuring light generated from the second light source; reflectance measuring means for measuring the reflectance of the measuring light with which the semiconductor region is irradiated; a third light guiding means for causing the measuring light reflected by the semiconductor region to be incident upon the reflectance measuring means; and change calculating means for receiving an output of the reflectance measuring means and calculating a change rate of reflectance of the measuring light by dividing the difference between the reflectances of the measuring light when the semiconductor region is irradiated and not irradiated with the exciting light by the reflectance of the measuring light when the semiconductor region is not irradiated with the exciting light.
This achieves the following effect. When the semiconductor region is irradiated with the exciting light guided by the first light guiding member, carriers in the semiconductor region are excited to produce an electric field. Under the influence of the electric field, the reflectance of the measuring light guided to the semiconductor region by the second light guiding member changes in the presence or absence of the radiation of exciting light. The change rate varies based on the magnitude of the intensity of the electric field and on the wavelength of the measuring light. If a defect serving as the center of recombination for carriers exists in a near-surface portion of the semiconductor region, the lifespan of the excited carriers is reduced, so that the intensity of the electric field formed by carriers is reduced. That is, the change rate of reflectance in the presence or absence of the radiation of exciting light changes based on the number of defects present in the near-surface portion of the semiconductor region. If there is a film on the semiconductor region, the process of capturing electrons proceeds with an increase in the thickness of the film so that the change rate of reflectance increases. If the change rate of reflectance of the measuring light in the semiconductor region is calculated by the change calculating means from the value measured by the reflectance measuring means, the change rate of reflectance includes data on the crystallized state of the semiconductor region, on the presence or absence of a film, or on the thickness of the film. Based on the change rate of reflectance, therefore, the surface state of the wafer can be evaluated with high sensitivity.
In the device for manufacturing a semiconductor device, the plurality of processing rooms include a processing room for performing a cleaning process involving an etching effect with respect to the wafer and a processing room for forming a film on the semiconductor region of the wafer. The arrangement allows optical evaluation in the situation in which the film has been removed from the wafer or in which a film has been formed on the wafer thereafter, thus allowing optical evaluation of the cleaned wafer surface without the natural oxide film.
The device for manufacturing a semiconductor device can further comprise an optical measurement room provided within the shared container, wherein the optical measuring means is disposed in the optical measurement room.
In the device for manufacturing a semiconductor device, the processing room for forming a film on the wafer is so constructed as to form an oxide film by performing a thermal oxidation process with respect to the semiconductor region of the wafer, the clustered device further comprising a processing room for forming a conductor film on the oxide film, the processing room being provided within the shared container. The arrangement allows the formation of the conductor film on the wafer formed with the thermal oxide film without exposing the wafer to the external space. Consequently, there can be formed a semiconductor device such as a MOS transistor having an oxide film with a small thickness which is controlled with high accuracy.
A first method of manufacturing a semiconductor device of the present invention includes formation of a film on a semiconductor region of a wafer or removal of a film from a surface of the semiconductor region of the wafer, the method comprising the steps of: (a) irradiating the semiconductor region of the wafer with measuring light; (b) intermittently irradiating the semiconductor region of the wafer with exciting light; and (c) calculating a change rate of reflectance by dividing the difference between the reflectances of the measuring light when the semiconductor region of the wafer is irradiated and not irradiated with the exciting light by the reflectance of the measuring light when the semiconductor region is not irradiated with the exciting light, wherein the thickness of the film is determined based on the change rate of reflectance.
In accordance with the method, data on the thickness of a film formed on the semiconductor region can be obtained by evaluation based on optical modulation reflectance spectroscopy by utilizing the phenomenon that the presence of the film in the semiconductor region under measurement performed by optical modulation reflectance spectroscopy causes the process of capturing electrons with an increase in the thickness of the film and hence increases the change rate of reflectance. In the measurement performed by ellipsometry currently used, a measurement error becomes extremely large or measurement sensitivity cannot be obtained at all if the film thickness is reduced to 4 nm or less. By contrast, optical modulation reflectance spectroscopy allows precise measurement of the thickness of such a thin film.
In the first method of manufacturing a semiconductor device, the step (c) includes producing a spectrum indicative of the change rate of reflectance when the wavelength of the measuring light is varied and determining the thickness of the film based on a peak value which is a maximum absolute value of the change rate of reflectance. This allows high-sensitivity measurement of the film thickness.
Alternatively, the step (c) includes producing a spectrum indicative of the change rate of reflectance when the wavelength of the measuring light is varied and determining the thickness of the film based on a peak-to-peak value which is the difference between a positive maximum value of the change rate of reflectance and a negative maximum value thereof. This allows highest-sensitivity measurement of the film thickness.
In the first method of manufacturing a semiconductor device, the step (c) includes determining the thickness of the film based on the change rate of reflectance at a constant wavelength close to the wavelength of the measuring light indicative of a peak value which is a maximum absolute value of the change rate of reflectance. This reduces the time required for the measurement of the film thickness.
In the first method of manufacturing a semiconductor device, even when the thickness of the film is 2 nm or less, which cannot be measured by the conventional optical measurement method, the film thickness can be measured with high sensitivity.
When the thickness of the film is 1 nm or less, in particular, the optical evaluation is performed with respect to a p-type semiconductor region as the semiconductor region. This provides high measurement sensitivity and high measurement accuracy.
In the first method of manufacturing a semiconductor device, the thickness of the film is measured in each of a p-type semiconductor region and an n-type semiconductor region as the semiconductor region. If the thickness of the film is measured to be 1 nm or less, the value measured in the p-type semiconductor region is used as the thickness of the film. If the thickness of the film is measured to be over 1 nm, the value measured in the n-type semiconductor region is used as the thickness of the film. As a result, the thickness of an extremely thin film can be measured with highest sensitivity by using the phenomenon that characteristics representing the relationship between the change rate of reflectance and the film thickness differ if the conductivity type of the semiconductor region is different.
In the first method of manufacturing a semiconductor device, the semiconductor region has preferably a resistivity of 0.1 xcexa9cmxe2x88x921 or less.
A second method of manufacturing a semiconductor device of the present invention is practiced by using a clustered device for manufacturing the semiconductor device, comprising a plurality of processing rooms, a shared container enclosing a space containing the plurality of processing rooms such that the space is held in an atmosphere disconnected from an external space, and transporting means for transporting the wafer within the shared container, the method comprising the steps of: (a) forming a film on the wafer or removing a film from a surface of the wafer in one of the plurality of processing rooms; and (b) determining the thickness of the film by optically evaluating a surface state of the wafer at any site in the shared container.
In accordance with the method, the thickness of the film on the wafer can be calculated by optical evaluation performed in the course of sequential process steps continuously performed or when the sequence of process steps are completed and an atmosphere of the external space is about to be restored. This allows a judgment of whether conditions for one of sequential process steps or for the entire process steps performed in the clustered manufacturing device are appropriate or not or a pass/fail judgment of the film formed on the wafer.
In the second method of manufacturing a semiconductor device, the step (b) includes the substeps of: (x) irradiating a semiconductor region of the wafer with measuring light; (y) intermittently irradiating the semiconductor region of the wafer with exciting light; and (z) calculating a change of reflectance by dividing the difference between the reflectances of the measuring light when the semiconductor region of the wafer is irradiated and not irradiated with the exciting light by the reflectance of the measuring light when the semiconductor region is not irradiated with the exciting light, so that the thickness of the film is determined based on the change rate of reflectance.
The method allows the determination of the thickness of an extremely thin film or of the presence or absence thereof in a clustered device by using the fact that data on the thickness of the film can be obtained by optical modulation reflectance spectroscopy, as described above.
In the second method of manufacturing a semiconductor device, the step (a) includes removing a natural oxide film from a surface of the wafer and the step (b) includes determining the thickness of the natural oxide film. As a result, an extremely thin natural oxide film with a thickness of several nanometers can be removed optimally.
In the second method of manufacturing a semiconductor device, there is further provided the step of (c) controlling the time of processing such that the natural oxide film remaining on the wafer has a thickness equal to or smaller than a specified value. As a result, the thickness of the natural oxide film can be held at a most preferred value.
In the second method of manufacturing a semiconductor device, the step (a) may include forming a gate insulating film on the wafer and the step (b) may include determining the thickness of the gate insulating film.
In the second method of manufacturing a semiconductor device, the step (a) may further include forming, on the gate insulating film, a conductor film for a gate electrode and the method may further comprise, after the step (b), the step of (c) controlling the thickness of the gate insulating film based on the change rate of reflectance calculated in the step (b) prior to the formation of the conductor film for a gate electrode.
In the second method of manufacturing a semiconductor device, the step (b) preferably includes measuring the change rate of reflectance in each of the p-type semiconductor region and the n-type semiconductor region and determining the thickness of a natural oxide film based on the dependent property of the p-type semiconductor region or the n-type semiconductor region providing the higher change rate of reflectance.